Thermally reversible superabsorbent polymers

Abstract

The invention provides a thermally reversible superabsorbent polymer adapted for use in melt processes, the polymer having a thermally reversible bond which is adapted to evanesce at an elevated temperature and revert to a thermally reversible bond upon cooling to ambient temperature so that the polymer is adapted, upon being heated to that elevated temperature, to dissociate into melt processable polymer fragments and, upon being cooled from that elevated temperature to ambient temperature, to re-associate. Also disclosed are superabsorbent polymer fibers and sheets formed from the thermally reversible superabsorbent polymer. The polymer fibers may be meltblown fibers which may be formed into a coherent nonwoven web. The meltblown fibers may include microfibers. The meltblown web may also include at least one type of secondary fiber, particulates or a mixture of fibers and particulates.

What is claimed is: 
     
       1. A superabsorbent polymer adapted for use in melt processes, said polymer having a thermally reversible bond which is adapted to evanesce at an elevated temperature and revert to a thermally reversible bond upon cooling to ambient temperature so that said polymer is adapted, upon being heated to said elevated temperature, to dissociate into melt processable polymer fragments and, upon being cooled from said elevated temperature to ambient temperature, to re-associate. 
     
     
       2. The polymer of claim 1 wherein said thermally reversible bond is an aromatic urethane bond. 
     
     
       3. The polymer of claim 1 wherein said elevated temperature is less than the degradation temperature of the polymer fragments. 
     
     
       4. The polymer of claim 1 wherein said polymer fragments have a higher melt flow rate than the re-associated polymer. 
     
     
       5. A superabsorbent thermally reversible polymer adapted for use in melt processes comprising: from about 70 percent to about 98.5 percent, by weight, of a soft segment selected from the group including: hydroxyl terminated water-soluble polymers and amine terminated water-soluble polymers; and     from about 1.5 percent to about 30 percent, by weight, of a hard segment including: at least one aromatic multifunctional isocyanate; and a chain extender having at least two functional groups capable of reacting with the isocyanate, at least one of the functional groups being a hydroxyl group attached to an aromatic ring.     
     
     
       6. The polymer of claim 5 wherein said chain extender is selected from the group including aromatic diols and aromatic triols having at least one aromatic hydroxyl group, and blends of at least one of said aromatic diols or triols with at least one aliphatic diols or aliphatic triols. 
     
     
       7. The polymer of claim 5 wherein said hydroxyl terminated water-soluble polymer is selected from the group including polyethylene oxide, copolymers of polymethylene oxide and polyethylene oxide, copolymers of polyethylene oxide and polypropylene oxide, and copolymers of polymethylene oxide and polypropylene oxide. 
     
     
       8. The polymer of claim 5 wherein said amine terminated water-soluble polymer is selected from the group including amine-terminated polyethylene oxide, amine-terminated copolymers of polymethylene oxide and polyethylene oxide, amine-terminated copolymers of polyethylene oxide and polypropylene oxide, and amine-terminated copolymers of polymethylene oxide and polypropylene oxide. 
     
     
       9. The polymer of claim 5 wherein said chain extender is substituted with at least one electron withdrawing substituent. 
     
     
       10. The polymer of claim 9 wherein said electron withdrawing substituent is selected from the group including nitrates, sulfonates, cyanates, esters, and amides. 
     
     
       11. The polymer of claim 5 wherein said chain extender is substituted with at least one electron donating substituent. 
     
     
       12. The polymer of claim 11 wherein said electron donating substituent is selected from the group including alkoxy groups, halides, alkyl and tertiary amines. 
     
     
       13. A superabsorbent polymer having the formula: ##STR3## wherein R 1  is selected from aliphatic and aryl groups; and wherein R 2  is selected from aliphatic and aryl groups so that said polymer has at least one R 2  which is an aryl group having from 6 to about 18 carbon atoms; x is an integer of from 2 to 20;   Z is selected from the group including:   --B--(P).sub.n --B--       where B is selected from oxygen, nitrogen, and sulfur;   P is a water-soluble polymer;   n is an integer of from 3 to 500; and   F is selected from: ##STR4## where R 3  is selected from substituted and unsubstituted aromatic groups and combinations of substituted and un-substituted aromatic and aliphatic groups so that said polymer is adapted, upon being heated to an elevated temperature, to dissociate into superabsorbent polymer fragments and, upon being cooled from said elevated temperature to ambient temperature, to re-associate.   
     
     
       14. The polymer of claim 13 wherein the water-soluble polymer "P" is selected from the group including polyethylene oxide, copolymers of polymethylene oxide and polyethylene oxide, copolymers of polyethylene oxide and polypropylene oxide, and copolymers of polymethylene oxide and polypropylene oxide. 
     
     
       15. The polymer of claim 13 wherein R 3  is selected from the group including aromatic groups substituted with at least one electron withdrawing substituent. 
     
     
       16. The polymer of claim 15 wherein R 3  is selected from the group including sulfonyldiphenyl, amino phenyl, benzoic acid, and phenyl acetic acid. 
     
     
       17. The polymer of claim 13 wherein R 3  is selected from the group including aromatic groups substituted with at least one electron donating substituent. 
     
     
       18. The polymer of claim 17 wherein R 3  selected from the group including thiodiphenyl, methyl phenyl and methoxy phenol. 
     
     
       19. Superabsorbent fibers formed from a superabsorbent polymer having a thermally reversible bond which is adapted to evanesce at an elevated temperature and revert to a thermally reversible bond upon cooling to ambient temperature so that said polymer is adapted, upon being heated to said elevated temperature, to dissociate into melt processable polymer fragments and, upon being cooled from said elevated temperature to ambient temperature, to re-associate. 
     
     
       20. The fibers of claim 19 wherein said thermally reversible bond is an aromatic urethane bond. 
     
     
       21. The fibers of claim 19 wherein said fibers are meltblown fibers. 
     
     
       22. The fibers of claim 19 wherein said meltblown fibers include microfibers. 
     
     
       23. The fibers of claim 19 comprising from about 1 percent, by weight, to about 80 percent, by weight, of one or more other materials selected from the group including wood pulp, natural fibers, synthetic fibers, particulates and superabsorbent particles. 
     
     
       24. A method of a forming superabsorbent fibers from a thermally reversible superabsorbent polymer comprising: heating a thermally reversible superabsorbent polymer to a temperature sufficient to dissociate the polymer into polymer fragments;   passing said polymer fragments through means for forming fibers; and   cooling said fibers to re-associate said polymer fragments.   
     
     
       25. The method of claim 24 wherein said temperature is less than the degradation temperature of the polymer fragments. 
     
     
       26. The method of claim 24 wherein said means for forming fibers is selected from meltblowing processes and spunbonding processes. 
     
     
       27. A superabsorbent sheet formed from a superabsorbent polymer having a thermally reversible bond which is adapted to evanesce at an elevated temperature and revert to a thermally reversible bond upon cooling to ambient temperature so that said polymer is adapted, upon being heated to said elevated temperature, to dissociate into melt processable polymer fragments and, upon being cooled from said elevated temperature to ambient temperature, to re-associate.   
     
     
       28. The sheet of claim 27 wherein said thermally reversible bond is an aromatic urethane bond. 
     
     
       29. The sheet of claim 27 wherein said sheet includes meltblown fibers. 
     
     
       30. The sheet of claim 20 wherein said meltblown fibers include microfibers. 
     
     
       31. The sheet of claim 27 comprising from about 1 percent, by weight, to about 80 percent, by weight, of one or more other materials selected from the group including wood pulp, natural fibers, synthetic fibers, particulates and superabsorbent particles. 
     
     
       32. A method of a forming a superabsorbent sheet from a thermally reversible superabsorbent polymer comprising: heating a thermally reversible superabsorbent polymer to a temperature sufficient to dissociate the polymer into polymer fragments;   passing said polymer fragments through means for forming a sheet; and   cooling said sheet to re-associate said polymer fragments.   
     
     
       33. The method of claim 32 wherein said temperature is less than the degradation temperature of the polymer fragments. 
     
     
       34. The method of claim 32 wherein said means for forming a sheet is selected from meltblowing processes, spunbonding processes and film extrusion processes.